The present invention relates to a process for preparing spheroidal silico-alumina particles.
The metallic oxides and particularly the mixtures of aluminium oxide and silicium oxide or silico-alumina, are widely used in the chemical industry. For most of these applications, silico-alumina is preferably used in the form of spheroidal particles or beads. Among the main advantages of these beads is better wear and crushing strength. Also, these beds may be more regularly distributed into the reactors, thereby reducing the pressure drop of the reactants passing through the reactors. In order to obtain metallic oxide beads of uniform sizes, a hydrosol of these oxides generally is introduced in droplets into a hot and practically water-immiscible fluid, acting as a gelling medium.
The application of this method to produce silico-alumina beads presents some drawbacks. Even if an alumina hydrosol is used as an alumina source, the gelling time of the silico-alumina mixture dispersed as droplets is particularly long and does not permit production of beads in a time period feasible for industrial application. To remedy such drawback, a gelling agent generally is used, most often a weak base. The obtained beads generally must be immediately subjected to an aging treatment. When compounds other than hyrosols are used as the alumina source, the addition of the gelling agent generally gives mixtures which prematurely stiffen and which cannot be dispersed as droplets into the gelling medium.
An object of the present invention is to provide a new method for preparing silico-alumina beads.
Another object of the present invention is to provide a method for producing silico-alumina beads employing alumina hydrogel.
A further object of the present invention is to provide a method for producing silico-alumina beads by the method of dispersion into a hot fluid, the wet beads obtained being workable and stable.
Still another object of the present invention is to provide a direct method for producing beads which, after drying and calcining, have a high mechanical strength and which can be used as catalysts or catalyst supports.